Gas permeation properties of ion-exchanged LTA-type zeolite membranes

NaA-type zeolite membranes were prepared on a 1.7-mm i.d. porous alpha -alumina tube by repeating a hydrothermal reaction. The membranes, which were prepared by four repetitions, were ion-exchanged with Ca2+ and K+, and the permeation for single-component and mixed gases were investigated at 35 degreesC. The NaA-type membrane showed a hydrogen permeance of (0.8-2.6) x 10(-8) mol m(-2) m(-1) Pa-1 and a hydrogen/n-butane ideal separation factor of 12-15. The permeability properties of the membrane for binary mixtures were dependent on the size of the permeating molecules and their adsorptivity to the zeolite. The KA-type zeolite membrane showed a higher ideal separation factor for a hydrogen/nitrogen system than did the NaA- and CaA-type zeolite membranes. The pores of the CaA-type zeolite membrane were larger than those in the NaA- and KA-type zeolite membranes, and showed higher permeances to n-butane and i-butane. All the zeolite membranes contained non-zeolitic pores, which decreased the selectivity of permeation.